The present invention relates to a high density magnetic recorder, and particularly to that provided with a magnetic recording disk wherein burst patterns are recorded for positioning magnetic head of the magnetic recorder.
Together with development of multi-media devices, recording density of magnetic recorders has become higher year by year. For realizing the higher recording density, the higher recording track density, that is, the narrower recording track pitch being required, a recording track pitch of 6000 TPI (Tracks Par an Inch), namely a track pitch of 4 .mu.m is attained today.
For recording and reading such high density recording tracks, high precision positioning of the magnetic head is indispensable. For that purpose, several methods have been proposed, one of which is a method of magnetic head positioning according to signals obtained by the magnetic head detecting a specific pattern, called the burst pattern, recorded on the magnetic recording media.
FIG. 4A illustrates a magnetic disk 1, in data cylinders 2 thereof the burst pattern 3 is recorded, as shown in FIG. 4B. In FIG. 4B, the right-left direction represents the rotating direction of the magnetic disk 1. The data cylinders 2 are composed of a plurality of data tracks 21, as shown in the left half of FIG. 4B, and on a part of which is recorded the burst pattern 3, the details thereof are illustrated in the right half of FIG. 4B.
In the example of FIG. 4B, the burst pattern 3 consists of four stripe strips 3A, 3B, 3C and 3D, adjacent with each other in the rotating direction. The defining width of a data track is 2P, and each of the four stripe strips 3A to 3D is composed of a sequence of a recorded area and a blank area each having a width 2P ranged in turn in the radial direction of the magnetic disk 1. The recorded areas are recorded, by a recording head provided for data recording, in such a manner that their pattern phases differ by 2P between the former two stripe strips 3A and 3B and the latter two stripe strips 3C and 3D, and by P between the second and the third stripe strips 3B and 3C, to be read out by a reproducing head H to be positioned.
In the example, signal intensity differences A-B and C-D are calculated, A to D being signal intensities obtained by the reproducing head H at the stripe strips 3A to 3D respectively. Each of the signal intensity differences A-B and C-D is to follow a quasi-sine curve having a cycle of 4P and a phase difference of P with each other, when radial position of the reproducing head H is changed. Thus, the radial position of the reproducing head H can be precisely specified and controlled in a width of 4P according to the signal intensity differences A-B and C-D.
However, the recording area having a radial width 2P can not be recorded by one writing, since the width of the recording head is generally designed to be narrower than the data track width 2P. Therefore, each of the recording areas of the burst pattern 3 should be recorded by two writings, shifting the recording head by a burst track pitch P, that is, 1/2 of the data track pitch 2P, and so, inevitably accompanied by an erase band 4 having an erase width e derived on each outer border line of burst tracks, 30 to 39 for example, as illustrated in FIG. 4B. The erase width e is determined by magnetic field distribution at edges of magnetic gap of the recording head and magnetic characteristic of the magnetic disk 1 such as crystal axis distribution in its recording layer.
When there are derived these erase bands 4 in the recorded areas of the burst pattern 3, there arise indifferent zones where both the signal intensity differences A-B and C-D do not vary even when the reproducing head H is shifted radially, disabling precise positioning of the reproducing head H.
In order to obtain a high S/N ratio, many magnetic recorders are provided with two magnetic heads, one high output MR (MagnetoResistive) head for reproducing and one ID (InDuctive) head for recording. Further, the width of the reproducing head is usually designed to be narrower than that of the recording head. So, the erase bands 4 derived by a wide recording head gives comparatively large effect for a narrow reproducing head, easily resulting in appearances of the indifferent zones.
That is a problem.